Stripping excess coating liquid from moving strip material

ABSTRACT

To prevent lateral displacement of excess coating liquid during gas jet stripping upon exit of a coated strip from a coating bath, baffles are provided at each edge of the strip adjacent the stripping gas nozzles, the baffles being urged towards the strip edges but restrained by followers in contact with the strip edges.

United States Patent [191 Marks et a1.

STRIPPING EXCESS COATING LIQUID FROM MOVING STRIP MATERIAL Inventors: Austin Cedric Marks, Mount Pleasant; Harold Vivian Cirson, Bulli, New South Wales, both of Australia John Lysaght (Australia) Limited, Sydney, New South Wales, Australia Filed: Aug. 3, 1971 Appl. No.: 168,721

Assignee:

Foreign Application Priority Data Aug. 13, 1970 Australia 2189 References Cited UNITED STATES PATENTS 11/1945 Sherman 118/63 X 1 July 3, 1973 2,888,901 6/1959 Nieman et a1. 118/103 2,967,114 1/1961 Mayhew 117/102 M X 3,140,960 7/1964 Grabczyk et al 1 18/122 3,681,119 8/1972 Reid et al. 118/63 X 3,032,006 5/1962 Kahn et a1. 118/63 UX 3,494,324 2/1970 Bauer et al. 1 18/63 X FOREIGN PATENTS OR APPLICATIONS 912,190 5/1954 Germany 117/102 R Primary Examiner-Morris Kaplan Attorney-Stevens, Davis, Miller & Mosher [57] ABSTRACT To prevent lateral displacement of excess coating liquid during gas jet stripping upon exit of a coated strip from a coating bath, baffles are provided at each edge of the strip adjacent the stripping gas nozzles, the bat"- fles being urged towards the strip edges but restrained by followers in contact with the strip edges.

8 Claims, 1 Drawing Figure 6 In 6, [ya/5 e a a I/Z 1 1 1 1 lll l 2a 1 I III l I I 2 {1% l K STRIPPING EXCESS COATING LIQUID FROM MOVING STRIP MATERIAL This invention relates to apparatus for stripping excess coating liquid from continuous strip material.

It is commonplace to strip excess coating liquid from continuous strip material, as it rises out of a clipping bath or other coating station, by directing gas streams or jets on to the coated surfaces laterally thereof and in a direction which is substantially normal thereto. The gas is usually air, superheated steam or other suitable media. The coating liquid may be paint, glue, molten metal or other common coating liquid, and the strip (to which the particular coating must, of course, be appropriate) may be paper, metal or other strip material pliant enough for reeling and amenable to production in long runs; for example, lengths running to thousands of feet.

Although the present invention is applicable to jet stripping in the general sense indicated above, it is pri marily concerned with excess coating removal near the edges of steel strip during the stripping of excess molten coating metal as the strip emerges substantially vertically from a molten metal bath, and the invention is described hereinafter mainly in terms of that particular use.

In continuous hot dip metal coating processes, one of the generally preferred methods of the prior art, to remove excess coating metal from the steel strip, is to arrange for the coated strip, as it leaves the molten metal coating bath, to move vertically through a zone containing the jet stripping means and, once the coating has solidified and the coated strip cooled, the coated strip is then reeled.

The jet stripping means comprises essentially a pair of linearly extending gas nozzles disposed substantially horizontally on either side of the strip, at a distance above the surface of the coating bath such that the coating on the strip is still molten upon arrival in the stripping zone. The lateral span of the stripping jets is normally greater than the width of strip passing between them. There may be substantial variations in the shape and design of nozzles, the jet span and gas pressure employed. The stripped matter simply flows downwardly from the stripping zone back to the bath. Jet stripping apparatus of the kind indicated above is hereinafter referred to as being of the type described.

A common occurrence in the use of apparatus of the type described is that a thicker coating remains on or near the edges of the strip than on the remaining area of the strip. In extreme cases the thicker coating may extend in from the edges by up to three inches but is normally confined to a marginal area within one-fourth inch from the edge. Behavior of the gas stream is complex. Our analyses indicate that this problem of extra edge margin thickness is associated with the tendency of the gas blast in the region of the strip edge to deflect in a direction laterally away from the direction of travel of the strip but substantially in the plane of the strip, rather than separating into an upward and downward component both substantially parallel to the direction of travel of the strip as normally occurs near the center line of the strip in the stripping zone; that is, the lateral stripe-like area of the blast impingement.

This appears to reduce the downwards stripping effectiveness of the blast in the marginal areas, resulting in retention of a greater thickness of coating in those areas than elsewhere on the strip surface.

The sideways component of the blast in the vicinity of the strip edges causes some molten metal to be blown sideways as well as downwards, and this sideways fraction leaves the strip roughly horizontally in the form of fine spray. This spray deposits on the jet nozzles and adjacent surfaces and can cause blockage of the slots from which the stripping jets emerge.

Molten metal forced to the edge of the strip and not completely removed solidifies and is retained causing rough and serrated edges; moreover, these rough edges and the more thickly coated margins of the strip militate against even and compact reeling of the cold coated strip.

In the area below the stripping zone, the blast directed at a downwards and outwards angle of say 30 to to the strip path, blows large splashes of molten metal off the strip which fall harmlessly onto the bath. These splashes however, can solidify and accumulate on the surface of the bath making necessary their removal by remelting or other means.

These adverse conditions due to outwards blast at the edge of the strip can be aggravated by any vertical misalignment which may exist between the jets, differences in jet pressure from the two nozzles, differences that may exist between the angles of tilt if the nozzles are arranged to direct the jets at an angle other than normal to the strip and variations in distance between the strip and the jets caused by either departures from flatness in the strip or flapping of the strip.

An object of the present invention is to ameliorate the disabilities referred to above by counter-acting sideways motion of the stripping blast in the vicinity of the strip edge margins and the stripping zone, so that a uniform vertical downwards pressure gradient is maintained across the full width of the strip (including the strip edge margins) thereby removing excess coating liquid in the marginal areas, or reducing thatexcess to an amount which is inconsequential.

A further object of the invention is to provide means counteracting this sideways component of the stripping blast which is capable of adapting itself to lateral movement of the sheet in its own plane during its feed past the jets, and flapping of the strip as it passes the jets.

The invention resides in one broad aspect in apparatus for stripping excess coating liquid from an upwardly moving strip comprising means for directing a lateral gas stream normally onto a coated surface of the strip characterized in that it includes an edge baffle comprising a baffle surface disposed substantially at right angles to the plane of the strip and extending longitudinally of the strip closely adjacent and parallel to one edge thereof at the region of impingement of the. gas stream, the baffle surface being mounted so as to permit movement thereof towards and away from said edge, means urging the baffle surface towards said edge, and means maintaining a minimum spacing between said surface and said edge.

Normally, one such baffle surface is provided on each side of the strip.

To facilitate the ready understanding of the invention and its practical implementation, it will now be described by way of example only with reference to the accompanying drawing which shows, in partly fragmentary isometric view, a baffle assembly incorporating the present invention.

In the drawing there is shown a steel sheet 1 rising vertically from a continuous hot dip coating bath and carrying, as described above, an excess of coating liquid. The strip 1 passes between a pair of linearly extending horizontal gas nozzles on either side of the strip for the removal of the excess coating in the manner described above. Since such nozzles are well known in the prior art, they are not shown in the drawing and no detailed description is required for the understanding of the present invention.

At each side of the moving strip there is provided, in accordance with the invention, a baffle 2 functioning to modify the flow of the stripping jets at the edges of the strip. Only one of the two baffles and its associated assembly is shown, since they are identical with each other.

The baffle plate 2 consists of an elongated strip of sheet steel or other plate material and has a straight vertical portion 2a extending beside the strip 1. This vertical portion is of course located at the region of impingement of the stripping jets on the moving strip. The baffle plate 2 is of such width as to more than span the greatest amount by which the strip may transversely depart from the mean strip path due to flapping movement of the strip or lack of flatness therein. The height of the vertical section of the plate 2 is such that it overlaps the area of impingement of the jet to a sufficient extent that it covers the height of the strip over which the jet is able to influence sideways departure of coating liquid from the strip.

The baffle plate 2 is mounted, by welding along its center, on a vertical supporting plate 3 bolted to a bracket 4 by means of rectangularly crossing elongated slots 5 and 6. These elongated slots enable the position of the baffle plate relative to the moving strip 1 to be readily adjusted both in the vertical and horizontal direction.

The bracket 4 is supported by a truck 7 provided with rollers 8 which are able to move freely along a pair of horizontal tracks 9 spanning the path of the moving strip 1.

Approach of the baffle plate 2 towards the edge of the moving strip beyond a desired minimum distance is prevented by means of a roller 10 mounted on the bracket 4, which bares against the adjacent edge of the strip 1. The roller 10 is provided with end flanges to assist in maintaining its engagement with the strip edge.

In cooperation with the roller 10, there must be provided means urging the baffle plate towards the edge of the strip 1. In the illustrated embodiment, this is provided by means of an arcuate lower portion 2b extending downwardly and outwardly away from the edge of the strip below the zone of impingement of the stripping jets. This baffle plate extension is shaped in an arc to correspond with the downward and sidewards components of the jet blast beyond the edge of the moving strip so as to avoid (as far as possible) accumulation of metal splashes on the face of the baffle plate. The flow of gas in the region of this curved surface creates a pressure differential between the front or strip side of the baffle plate and the back thereof, resulting in a thrust which urges the baffle plate towards the strip edge. It is found in practice that this baffle loading effect is quite substantial, and that the baffle will return inwards towards the strip if drawn or knocked outwardly, for example, due to sideways motion of the moving strip.

From the foregoing it will be understood that in operation, the baffle plate will be continually urged towards the edge of the strip so that a predetermined minimum distance is maintained between these two elements as the roller 10 follows the edge of the strip 1.

The curved extension 2b of the baffle plate has the additional advantage that it enables the baffle to be temporarily forced outwardly of the strip when struck by protruding portions of the strip, such as occur, for example, at joins between successive coils of strip.

While the outward curvature of the portion 2b minimizes the buildup of deposits by splashing of coating metal, this may be further reduced by making the baffle from a metal having a high thermal conductivity, such as brass. The baffle, being constantly chilled by an air blast, enables the splashes to solidify rapidly and fall harmlessly down into the molten metal bath.

It is important in the practice of the invention that the baffle surface be approximately normal to the adjacent edge of the strip and extend a short distance above and below the stripping zone in order to maintain a pocket of stagnation pressure in this region. This pressure is established by an adjustment of the distance of the bafi'le surface from the edge of the strip depending on the circumstances of jet pressure, angle of tilt and other factors which determine the force of the dead wood component of the jets. As has been mentioned above, the width of the baffle surface should be at least sufficient to maintain a pocket of stagnation pressure adjacent to the edge of the strip despite variations in the distance between the strip and the jet nozzles caused by lack of flatness of the strip or flapping.

It will be appreciated that the present invention is capable of embodiments in many forms other than that illustrated. The mounting means provided for the baffle plate may take many forms. For example, the plate may be fixed on the free end of a swingable arm pivoted by its other arm at a considerable distance from the stripping zone; a distance such that during any normal working movement of the plate towards or away from the strip edge, the baffle surface of the plate remains, for all practical purposes, substantially parallel to that edge. Alternatively, the plate may be mounted on one arm of a parallelogram linkage, in which case the plate will rise or fall a little, relative'to the stripping zone, when it moves translationally, but will remain parallel with the strip edge.

The loading means for the baffle plate may consist of a light loading spring attached to the truck 7 or of making the rails 9 slightly tilted so that the truck tends to run downhill towards the adjacent edge of the moving strip.

Instead of the roller 10, the following means which maintain the baffle surface at its minimum spacing relative to the adjacent strip edge may consist of a skid which rides that edge or some other suitable device.

These and other variations within the spirit and scope of the present invention will be apparent to the skilled reader, and it will be clear that the invention is not restricted by such embodiments as have been described, but should be accorded its true ambit in accordance with the claims which follow.

We claim:

1. Apparatus for stripping excess coating liquid from an upwardly moving strip comprising means for directing a lateral gas stream normally onto a coated surface of the strip wherein the improvement comprises an edge baffle comprising a baffle surface disposed substantially at right angles to the plane of the strip and extending longitudinally of the strip closely adjacent and parallel to one edge thereof and over the longitudinal extent of the region of impingement of the gas stream, the baffle surface being mounted so as to permit movement thereof towards and away from said edge, means urging the baffle surface towards said edge, and means maintaining a minimum spacing between said surface and said edge.

2. Apparatus as claimed in claim 1, further characterized in that said means urging the baffle surface towards said edge is thrust generated on a longitudinal extension of the baffle surface by the passage past said extension of gas from said stream after deflection by the coated surface.

3. Apparatus as claimed in claim 2, wherein said extension is shaped so as to generate, with deflected gas from said stream, a region of low pressure at its surface facing said edge.

4. Apparatus as claimed in claim 3, wherein said extension is curved downwardly and outwardly from said edge below the said region of impingement of said gas stream.

5. Apparatus as claimed in claim 1 wherein the baffle surface is of a width greater than the extent of transverse departures from the mean path thereof occurring adjacent the baffle surface.

6. Apparatus as claimed in claim 1 wherein said means maintaining a a minimum spacing comprises follower means adapted to engage said edge to prevent the baffle approaching said edge beyond said minimum spacing.

7. Apparatus as claimed in claim 6 wherein said follower means is a roller.

8. Apparatus as claimed in claim 1, in which the baffle surface comprises a metal having a high thermal conductivity. 

1. Apparatus for stripping excess coating liquid from an upwardly moving strip comprising means for directing a lateral gas stream normally onto a coated surface of the strip wherein the improvement comprises an edge baffle comprising a baffle surface disposed substantially at right angles to the plane of the strip and extending longitudinally of the strip closely adjacent and parallel to one edge thereof and over the longitudinal extent of the region of impingement of the gas stream, the baffle surface being mounted so as to permit movement thereof towards and away from said edge, means urging the baffle surface towards said edge, and means maintaining a minimum spacing between said surface and said edge.
 2. Apparatus as claimed in claim 1, further characterized in that said means urging the baffle surface towards said edge is thrust generated on a longitudinal extension of the baffle surface by the passage past said extension of gas from said stream after deflection by the coated surface.
 3. Apparatus as claimed in claim 2, wherein said extension is shaped so as to generate, with deflected gas from said stream, a region of low pressure at its surface facing said edge.
 4. Apparatus as claimed in claim 3, wherein said extension is curved dowNwardly and outwardly from said edge below the said region of impingement of said gas stream.
 5. Apparatus as claimed in claim 1 wherein the baffle surface is of a width greater than the extent of transverse departures from the mean path thereof occurring adjacent the baffle surface.
 6. Apparatus as claimed in claim 1 wherein said means maintaining a minimum spacing comprises follower means adapted to engage said edge to prevent the baffle approaching said edge beyond said minimum spacing.
 7. Apparatus as claimed in claim 6 wherein said follower means is a roller.
 8. Apparatus as claimed in claim 1, in which the baffle surface comprises a metal having a high thermal conductivity. 